1. Field of the Invention
The disclosures herein relate generally to bone anchorage implants and more particularly to a screw form dental implant having a combination of features designed to produce bone condensation while insertion is easy.
2. Description of the Related Art
Many current screw-form dental implants are well designed for use in dense bone. For example, the implant disclosed in U.S. Pat. No. 5,897,319 has sharp cutting features at their apical ends that readily facilitate self-tapping into hard bone.
The osseous anatomy of the human jaw is complex. While the density of the bone in the anterior regions of the mandible and maxilla is high, the posterior regions, particularly in the maxilla, are of significantly lower density. The height of the bony ridge in the posterior maxilla can be greatly reduced in partially or totally edentulous patients. This can lead to the need for use of shorter dental implants or grafting procedures in order to increase the height of bone available for implant placement.
Dental implant stability in low-density bone, such as that found in the posterior regions of the mandible and maxilla and in regenerated bone, can be difficult to achieve. Compaction of low density bone, such as by the user of osteotomes, is commonly performed in order to enhance the stability of implants at the time of surgical placement.
Implants of various tapers and with various thread profiles are known in the art. For example, U.S. Pat. No. 5,427,527 describes a conical implant design that is placed into a cylindrical osteotomy site in order to induce bone compression at the coronal aspect of the implant, i.e., at its widest end.
A variety of thread profiles and patterns are known in the art. The most common design involves a symmetrical, V-shaped appearance such as that illustrated in U.S. Pat. No. 5,897,319. A variable thread profile is disclosed in U.S. Pat. Nos. 5,435,723 and 5,527,183 which is mathematically optimized for stress transfer under occlusal loads. U.S. Pat. Nos. 3,797,113 and 3,849,887 describe dental implants with external thread-like features having flat shelf facing the coronal end of the implant. U.S. Pat. No. 4,932,868 discloses a thread design with a flat surface disposed toward the apical end of the implant. This thread is not variable over different points of the implant and does not produce both cutting and compression actions as described herein. U.S. Pat. No. 5,007,835 discloses a screw-type dental implant with rounded threads for providing controlled radial osteocompressive force against the walls of a pre-tapped bone site. U.S. Pat. No. 5,628,630 discloses a method for designing dental implants to optimize and control stress transfer to surrounding bone including a thread design that changes from a sharp, highly angled profile at the apical end of the implant to a flat, nearly square profile at the coronal end, the goal being to control the surface area presented to occlusal forces. U.S. Pat. No. 6,402,515 describes a condensing implant with a gradually enlarged thread width to enhance stability in low density bone.
As an implant is designed to be more condensing its insertion becomes a more difficult. It is also more difficult to control the position of the implant since a condensing implant has a stronger tendency to slip into a region with the lowest bone density.
Therefore, what is needed is an implant that enhances stability in low density bone such as that formed in the posterior mandible and posterior maxilla but is easily inserted and can be used also in regular bone and in hard bone. It is also needed that the implant will keep its path of insertion and will not slip towards regions with low bone density.